1. Field of the Invention
The present invention relates data transmission methods in a multiple-input, multiple-output (MIMO) wireless transmission system, and particularly to an optimal power allocation method for layered-steered space-time coded (LSSTC) wireless transmissions.
2. Description of the Related Art
Various techniques have been proposed to counter the problem of propagation conditions and to achieve data rates that are very close to the Shannon limit. One of these techniques employs MIMO systems, which use antenna arrays at both the transmitter and the receiver. Wolniansky et al. have proposed the well-known MIMO scheme known as V-BLAST (see “V-BLAST: An Architecture for Realizing Very High Data Rates Over the Rich-Scattering Wireless Channel”, Proc. ISSSE-98, URSI International Symposium (1998), pp. 295-300). In V-BLAST, parallel data streams are sent via the transmit antennas at the same carrier frequency. V-BLAST can achieve high spectral efficiencies without increasing the system's bandwidth or transmitted power. While MIMO systems, such as V-BLAST, can improve the system capacity greatly, it is difficult to implement antenna arrays on handheld terminals due to size, cost and hardware limitation. Moreover, V-BLAST has poor energy performance and doesn't fully exploit the available diversity. In order to overcome these problems, space-time block code (STBC) was developed. STBC has two transmit and one receive antennas that provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit and two receive antennas. This scheme can be generalized to two transmit antennas and M receive antennas to provide a diversity order of 2M.
With the tempting advantages of V-BLAST and STBC, many researchers have attempted to combine these two schemes to result in a multilayered architecture called MLSTBC, in which each layer is composed of antennas that correspond to a specific STBC. This combined scheme arises as a solution to jointly achieve spatial multiplexing and diversity gains simultaneously. With the MLSTBC scheme, it is possible to increase the data rate while keeping a satisfactory link quality in terms of symbol error probability (SER). Beamforming has been combined with MLSTBC to produce a hybrid transmission scheme called the layered steered space-time codes (LSSTC). The addition of beamforming to MLSTBC further improves the performance of the system by focusing the energy towards one direction, where the antenna gain is increased in the direction of the desired user while reducing the gain towards the interfering users.
However, the problem of efficient power allocation to ensure a low error rate in an LSSTC system still exists. Thus, an optimal power allocation method for an LSSTC wireless transmission system solving the aforementioned problems is desired.